Hexafluorosilicic acid

• Hydrofluosilicic
• Hexafluorosilicic
• Fluorine silica
• Fluorine silicon hydride
• Pebble hydrofluoric acid

Colorless liquid

Liquid

1.38 g · cm -3 ( 35proz. solution)

-30 ° C ( 35proz. solution)

110 ° C ( decomposition)

Miscible with water

Risk

430 mg · kg -1 ( LD50, rat, oral)

Template: Infobox chemical / molecular formula search available

Hexafluoridokieselsäure is a chemical compound that is known only in aqueous solution and strongly acid reaction. When attempting to complete dehydration it decomposes to hydrofluoric acid and silicon tetrafluoride. They can be isolated as the dihydrate, which melts at 60 ° C with decomposition. The salts of the Hexafluoridokieselsäure (eg Magnesiumhexafluoridosilicat Mg [ SiF 6 ], Natriumhexafluoridosilicat Na2 [ SiF 6 ] or Zinkhexafluoridosilicat Zn [ SiF 6 ] ) are called Hexafluoridosilicate.

Production and representation

Hexafluoridokieselsäure produced during reaction of hydrofluoric acid with silicon dioxide ( quartz, sand, ...)

Or by mixing of water with silicon tetrafluoride.

It is also formed as a byproduct in the digestion ( the reaction for the preparation of phosphorus) of fluorapatite with sulfuric acid, hydrofluoric acid is formed, which reacts with the silicates contained in the fluoride apatite in varying amounts as an admixture. As Hexafluoridokieselsäure must be disconnected from phosphorus, it has been found as a cheap by-product different applications.

Properties

Hexafluoridokieselsäure is a colorless liquid that is cleaved in anhydrous state at room temperature is already about 50% in Siliciumtetraflurorid and hydrogen fluoride. Be distilled without decomposition proc only 13.3. aqueous solution. The Hexafluoridosilikatanion SiF62 - in contrast to the other Hexahalogenidosilikaten stable to hydrolysis.

Use

Hexafluoridokieselsäure is used as a disinfectant and preservative of wooden poles and Gerbebrühen, for cleaning copper and brass kettles in breweries, the acid polishing of crystal glass and for the production of metal oxide films. Furthermore, it is used as a reagent in organic synthesis to cleave Si -O bonds with silyl ethers. In the United States, the connection is frequently (in a caries prophylaxis) used for fluoridation of water. The acid and its salts are used as for the surface treatment fluates ( Fluatierung concrete ) to cure the surface to make water-impermeable. They are therefore referred to as a stone crystallizers.